Process for producing metal compounds from graphite oxide

ABSTRACT

A process for providing elemental metals or metal oxides distributed on a carbon substrate or self-supported utilizing graphite oxide as a precursor. The graphite oxide is exposed to one or more metal chlorides to form an intermediary product comprising carbon, metal, chloride, and oxygen This intermediary product can be flier processed by direct exposure to carbonate solutions to form a second intermediary product comprising carbon, metal carbonate, and oxygen. Either intermediary product may be further processed: a) in air to produce metal oxide; b) in an inert environment to produce metal oxide on carbon substrate; c) in a reducing environment to produce elemental metal distributed on carbon substrate. The product generally takes the shape of the carbon precursor.

This application is a divisional of Ser. No. 08/833,107, filed Apr. 4,1997, now U.S. Pat. No. 5,876,687.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention pertains generally to the art of producing metal or metaloxides distributed in a porous carbon substrate or self-supported andmore specifically to producing such compounds wherein graphite oxide isused as one of the original materials.

2. Description of the Related Art

In the art it is known to provide graphite oxide having foreign organicchemicals inserted therein. For the most part, the organic chemicals areonly absorbed by the graphite oxide and do not break the chemical bondsin the graphite oxide. However, exposure of the graphite oxide to H₂ Sor CH₃ OH, for example, may result in chemical reactions between thegraphite oxide and the organic chemicals to produce organic derivativesof graphite oxide.

Graphite oxide may also be partially reduced by a number of commonreducing agents to produce graphite, although complete reduction has notbeen observed.

Metal oxides, porous or fibrous, may be produced in a sol-gel processwhich uses metal alkoxide, an organo-metallic compound, to produce aporous metal oxide (or ceramic) compound. After hydrolysis andpolymerization, the material is treated by other physical processes(e.g., coating spinning, gelling, precipitation) and then heated toobtain the desired product.

Impregnation of chemical solutions in porous or activated carbon mayproduce carbon containing metal compounds. Such products are generallycarbon with less than 10% by weight of the metal components.

Heating graphite oxide in an inert environment causes thermaldecomposition at 150° C.-200° C. If the heating rate is high, theproduct is a very fine, about 20 Å, carbon powder. If the heating rateis low, then the graphite oxide does not disintegrate, but H₂ O, CO, andCO₂ are released, and the product is a graphite-like carbon materialwhich contains a substantial quantity of oxygen. This indicatesincomplete thermal decomposition during slow heating to 200° C.

Attempts have also been made to provide reaction products similar tothose obtain by the inventive processes using graphite fluoride as aninitial reactant.

With reference to the above discussion of the related, it should benoted that graphite fluoride reacts with other chemicals generallyaround 200° C. to 450° C., although reaction with AlCl₃ may occur attemperatures around 150° C. Fluorine compounds are released during thereactions, which are highly corrosive at such temperatures.

Further, Hennig (1959) summarized the known organic derivatives ofgraphite oxide. Considering graphite oxide as an organic compoundcontaining the functional groups --OH and ═O, Hennig suggested thatgraphite oxide could react with organic compounds which are generallyreactive to these functional groups. His summary indicates that exceptfor the partial reduction of graphite oxide to graphite by reducingagents, these functional groups are surprisingly inactive.

The sol-gel process is expensive because of its complexity and highprice of the reactant.

Lastly, the products from carbon impregnation have low concentrations ofnon-carbon materials.

The present invention overcomes the foregoing difficulties encounteredin the art in a way which is simple and efficient, while providingbetter and more advantageous results.

SUMMARY OF THE INVENTION

In accordance with the present invention, a new and improved process forproducing a carbonaceous material comprising metal compounds fromgraphite oxide is provided.

More particularly, in accordance with the invention, the processcomprises the step of exposing the graphite oxide to a metal chloride ator below the thermal decomposition temperature of the graphite oxide fora time sufficient to obtain an intermediary carbonaceous reactionproduct comprising metal, oxygen, and chlorine.

According to one aspect of the invention, the "graphite oxide" includesthose made from amorphous carbon (such as pitched based carbon fibers oractivated carbon) through typical processes of making graphite oxide.The graphite oxide-like material made in this lab from amorphous carbonare structurally less orderly and contains less oxygen than thetraditional graphite oxide, which is made from crystalline graphite.However, they are perfect reactants for the reactions described in thisinvention.

According to another aspect of the invention, the process furthercomprises the step of placing the intermediary carbonaceous product inaqueous solution containing potassium carbonate (K₂ CO₃) or sodiumcarbonate (Na₂ CO₃) to remove chlorine and obtain another intermediarycarbonaceous product containing metal, oxygen, and carbonate. This stepis optional but is essential in the cases where the above-describedmetal chlorides are hygroscopic in ambient air or inert to oxygen orcarbon at its melting point.

According to another aspect of the invention, the process furthercomprises the step of heating the intermediary carbonaceous reactionproducts in a reducing environment to remove the chlorine or carbonateand oxygen to produce a reaction product of carbon and metal.

According to another aspect of the invention, the process furthercomprises the step of heating the carbonaceous reaction product in aninert environment to remove the chlorine to produce a carbonaceousreaction product containing metal oxide particles.

According to another aspect of the invention, a process for producing ametal oxide from graphite oxide comprises the steps of exposing thegraphite oxide to a metal chloride at a temperature below 200° C. for atime sufficient to form an intermediary carbonaceous material comprisingthe elements of metal, chlorine, and oxygen; (optionally) placing thisintermediary product in aqueous solution containing potassium carbonate(K₂ CO₃) or sodium carbonate (Na₂ CO₃) to remove chlorine and obtainanother intermediary carbonaceous product containing metal, oxygen, andcarbonate; and, heating the intermediary carbonaceous material in air ata temperature of at least 300° C. for a time sufficient to oxidize andremove carbon and chlorine or carbonate to produce the metal oxide.

One advantage of the present invention is the use of graphite oxide as aprecursor for further processing rather than graphite fluoride. Graphiteoxide is safer, easier to produce, and less expensive than graphitefluoride.

Another advantage of the present invention is the mild conditions forthe reaction between the graphite oxide and the metal chloride. In manycases, the reaction can occur in water solution.

Another advantage of the present invention is that the reaction productscontain a large quantity of small particles. Therefore when the finalproduct is ceramics, the yield is high, and the surface area is large.

Another advantage of the present invention is that the process does notrequire expensive organo-metallic compounds as reactants to producegamma-Al₂ O₃ having a surface area of 80 m² /g.

Yet another advantage of the present invention is that the ceramic orcarbon containing ceramic products take the form of the carbonprecursor. Therefore, the final product may be in the form of a powder,fiber, or fabric.

Still other benefits and advantages of the invention will becomeapparent to those skilled in the art upon a reading and understanding ofthe following specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement ofparts. A preferred embodiment of these parts will be discussed in detailin the specification and illustrated in the accompanying drawings, whichform a part of this disclosure and wherein:

FIG. 1 is a schematic representation of the general processes accordingto the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

It will be understood that the specific embodiments described herein aremerely illustrative of the general principles of the invention and thatvarious modifications are feasible without departing from the spirit andscope of the invention.

With reference to FIG. 1, in the inventive process described herein,graphite oxide is formed by processes known in the art. The preferredembodiment of the invention uses the method developed by Hummers andOffeman (1958), although graphite oxide obtained by other processes maybe used. The original carbon materials used to make graphite oxide maybe crystalline graphite, amorphous carbon, or graphitized carbon. Theymay be in the form of powder or fibers.

The graphite oxide thus obtained is then used as a template for furtherprocesses which will be addressed in detail in this specification.

Generally, the graphite oxide is exposed to a metal chloride at or belowthe thermal decomposition temperature of the graphite oxide to produce acarbonaceous material including the elements of the metal, oxygen andchlorine, hereinafter C(M,O,Cl). The metal chloride, hereinafter MCl,may be in the form of solution, pure liquid, pure vapor, or a mixture ofthe above forms. The BET surface area (in nitrogen) of the C(M,O,Cl) isgenerally less than 4 m² /g due to the presence of the non-carbonmaterials.

The chlorine in the C(M,O,Cl) can be removed by placing the carbonaceousproduct in aqueous solution containing potassium carbonate (K₂ CO₃) orsodium carbonate (Na₂ CO₃). This produces a carbonaceous productcontaining metal carbonate and oxygen, hereinafter C(MCO₃,O).

The C(M,O,Cl) and C(MCO₃,O) may then be subjected to further processing.In one preferred embodiment, the C(M,O,Cl) or C(MCO₃,O) is heated in airat a temperature of 250° or higher to remove the carbon and chlorine byoxidation. The metal is converted to metal oxide. The metal oxide thusobtained has a large surface area which suggests its usefulness as acatalyst, solar cell, or gas sensor.

In another preferred embodiment, the C(M,O,Cl) or C(MCO₃,O) is placed ina reducing environment. The product thus obtained is a carbonaceousmaterial having metal particles therein. The product is potentiallyuseful in the area of batteries and catalysts.

In yet another preferred embodiment, the C(M,O,Cl) or C(MCO₃,O) isheated in an inert environment of, for example, nitrogen or argon. Thepreferred temperature is greater or equal to 700° C. In nitrogen, thepreferred range is from approximately 700° C. to approximately 1200° C.In argon, the temperature range may be expanded as high as approximately1800° C. This process completely removes, or significantly reduces theamount of chlorine or carbonate in the product. The product thusobtained is a carbonaceous metal oxide having a large BET surface areasuggesting its usefulness in the area of batteries and catalysts.

The products formed by the above processes take the shape of the carbonprecursor whether it be powder, fiber or fabric.

The invention is more particularly described in the examples thatfollow. However, it should be understood that the present invention isby no means restricted by these specific examples.

EXAMPLE I

Graphite oxide made from commercially purchased crystalline graphitepowder (325 mesh) was exposed to an excess quantity of AlCl₃, alsocommercially purchased, at a temperature histogram as follows: At 120°C. for 18 hours, then up to 185° C. in 6 hours, then at 185° C. for 20hours, then up to 230° C. in five minutes, then at 230° C. for 15minutes, before removing the reaction product from the reactor.Elemental analysis indicated that the O:C atomic ratio was approximately1.4, where the oxygen atoms were either a part of the graphite oxide ora part of water. The final temperature at 230° C. for a short time wasused to evaporate the unreacted AlCl₃ (boiling point 183° C.).

The initial reaction product, C(M,O,Cl), was subjected to elementalanalysis for bulk composition, X-ray photoelectron spectroscopy (XPS)for surface analysis, and X-ray diffraction (XRD) for structureanalysis. The elemental analysis data indicated the bulk Al:C atomicratio was 0.23. The XPS data indicated the surface Al:C atomic ratio was0.32. The XRD data showed no peak at all, indicating a highlydisordered, or amorphous structure. The energy dispersive spectrum (EDS)data, which detect and analyze the chemical elements of the sample inthe region within 3 microns from the surface, indicated that the Al:Clatomic ratio was about 1:3. This indicated that the chlorine atoms thatcame to this carbonaceous material in the form of AlCl₃ mostly stayed inthe final product. It is believed that the high concentration ofnon-carbon elements distorted the orderly structure of graphitecrystals. The BET surface area of reaction product C(M,O,Cl) wasdetermined to be 3 m² /g.

In one embodiment of the invention, the C(M,O,Cl) was subjected toheating in an inert environment. Specifically, heating C(M,O,Cl) in1000° C. nitrogen yielded a reaction product having a BET surface areaof 75 m/² /g. XRD of reaction product showed peaks of graphite andgamma-Al₂ O₃, indicating a carbonaceous material containing metal oxide.

It is believed that some of the non-carbon materials as well as a smallamount of carbon were removed from the interior of the C(M,O,Cl) duringthe heating process which resulted in the increased surface area andrestored carbon structure.

Quickly heating the C(M,O,Cl) to 1800° C. in argon resulted in a productthat contained a large quantity of Al, a small amount of O, and a numberof impurities.

In a further embodiment of the invention, the C(M,O,Cl) was burned inair at 400° C. for 109 hours, then 500° C. for 108 hours, and finally600° C. for 39 hours until complete oxidation was obtained. The reactionproduct was characterized by a BET surface area of 80 m² /g. XRDrevealed gamma-Al₂ O₃ only, indicating a metal oxide. It is believedthat the high surface area of this reaction product suggests potentialuse as a catalyst or gas sensor.

EXAMPLE II

Graphite oxide prepared from a commercially purchased amorphous carbonpowder (325 mesh) was exposed directly to bromoform solution containingAlCl₃ at 100° C. for 115 minutes. The XRD data indicated that the"amorphous" carbon contained a small amount of crystalline graphite. TheC(M,O,Cl) obtained was rinsed with cold distilled water beforecharacterization. According to XRD, the molecular structure of thegraphite oxide disappeared and no new XRD peaks were formed. Accordingto EDS data, the reaction product was carbon containing Al and Cl. Somebromine from the solvent was also present. The EDS data suggest theAl:Cl:Br atomic ratio was approximately 2:1:1, and the Al:C ratio was atleast 1:6.

EXAMPLE III

Graphite oxide prepared from a commercially purchased amorphous carbonpowder (325 mesh) was exposed directly to bromoform solution containingAlCl₃ at room temperature for 115 minutes. As in EXAMPLE II, thereaction product was rinsed in cold distilled water. Similar to EXAMPLEII, the molecular structure of the graphite oxide was destroyed.However, this reaction product contained very little, if any, bromine.Instead, XRD of the reaction product revealed highly crystallineAlCl₃.6H₂ O. The EDS suggest that the Al:C ratio was at least 1:3.

EXAMPLE IV

Graphite oxide prepared from a commercially purchased crystallinegraphite powder (325 mesh) was exposed directly excess quantities ofboth I₂ and LiCl at 130° C.-150° C. for 22 hours, then heated in 184°C-194° C. for 2 hours to remove unreacted I₂. XPS data of the reactionproduct indicated its surface was such that the atomic C:Li:Cl was1:0.08:0.14. Elemental analysis indicated that its bulk was such thatthe atomic C:LI:Cl was 1:4.4:4.5. The XRD data showed sharp and highpeaks for both LiCl and LiCl.H₂ O. These data suggest that thecarbonaceous product being studied had a surface that was mostly carbon.But, in the interior, the carbon in this "carbonaceous material"actually contained much more LiCl than carbon itself. The product wasquickly rinsed and dried in 150° C. nitrogen. The rinsed reactionproduct was then examined by XRD and EDS. The XRD indicated the presenceof LiCl.H₂ O. It is believed that the LiCl.H₂ O was located at theinterior of the carbon material because surface LiCl would have beeneasily removed by the rinsing process. EDS data shows the presence of alarge quantity of chlorine. (EDS does not provide information on lithiumbecause it is an element lighter than boron.) According to the EDS data,the chlorine to carbon ratio was at least 1:4.

Part of this product was further rinsed in ethanol at room temperature.The process appears to dissolve most of the non-carbon elements. Nothingbut trace amounts of non-carbon elements were detected by EDS.

Instead of rinsing with ethanol part of this product was rinsed againwith water for 3 more times. The sample lost 86% of its weight duringthese 4 times of water rinsing. EDS data again indicated the presence ofonly traces of the non-carbon elements.

These results suggest that the LiCl in the carbon, although not on thesurface, can be reached and dissolved by a number of different solvents.The dissolvation can be nearly complete if the solvent quantity islarge, and the time for dissolvation is sufficiently long.

EXAMPLE V

A sample of graphite oxide prepared according to Example IV was exposedto a water solution containing LiCl at 100° C. The reaction product thusobtained was similar to the reaction product obtained in Example IV inthat the carbon contained lithium and chlorine. The EDS data suggeststhat the chlorine to carbon ratio was at least 1:4.

EXAMPLE VI

Another sample of graphite oxide prepared according to Example IV wasexposed to a water solution containing saturated ZnCl₂ at 130° C. foreight hours, then 170° C. for 37 hours. This reaction product was carboncontaining ZnCl₂. Further treatment of this reaction product in air at300° C. for 13 hours, then 350° C. for 70 hours, then 400° C. for 74hours, produced ZnO powder having a surface area of 30 m² /g, indicatingfull oxidation.

An alternate embodiment of the invention produces doped products byexposing the graphite oxide to a mixture of several metal chlorides. Thedopant(s) can be added to the reactants either as impurities, aselements or as compounds.

EXAMPLE VII

The gamma-Al₂ O₃ of EXAMPLE I was successfully observed by SEM withoutmetal or carbon coating, therefore, it is not an insulator. Theconductivity of this product is believed to come from the small amountof potassium present in the gamma-Al₂ O₃. The potassium came from KMnO₄which was used in the process of making the graphite oxide fromgraphite. The presence of potassium in the gamma-Al₂ O₃ suggests thatdoped graphite oxide may be obtained by mixing the dopant into thereactants before the graphite oxide is formed from the graphite. It isalso suggested that doped graphite fluoride could be formed by addingthe dopant(s) before forming graphite fluoride by methods known in theart.

EXAMPLE VIII

A experiment similar to the first part of Example I was conducted,except that the graphite oxide was prepared from commercially purchasedactivated carbon having a BET surface area of 1100 m² /g, and that itsreaction to AlCl₃ had a temperature histogram of 120° C. for 18 hours,140° C. for 1 hour, 160° C. for 3 hours, 170° C. for 2 hours, 180° C.for 9 hours, 193° C. for 9 hours, and 225° C. for 0.2 hour.

The carbonaceous materials thus formed were found to be amorphous (XRDanalysis) with an atomic O:C ratio of about 0.5. (The oxygen atomsinclude those from water.) The surface area was 30 m² /g.

According to EDS data, after the reaction with AlCl₃, the atomic Al:Cratio was about on fourth of that obtained in Example I, but its atomicAl:Cl ratio was about 2.5 times that obtained from Example I. Theseresults indicate that, contrary to Example I much of the chlorine atomsthat come to this carbonaceous material in the form of AlCl₃ were notpresent in the product.

EXAMPLE IX

An experiment similar to Example IV was conducted, except that thegraphite oxide was prepared with its non-carbon reactants (KMnO₄, NaNO₃,and H₂ SO₄) at 500% of the quantities described in the process byHummers and Offeman (1958).

After the reaction with excess quantities of LiCl and iodine, theproduct was soaked and mixed in distilled water in a test tube. Thevolume of distilled water utilized was approximately the same as thebulk volume of the carbonaceous material. This mixture was then placedin a centrifuge for separation. Excess water which was clear andcontaining no carbonaceous product was then quickly removed. The wetproduct was then dried in 120° C. nitrogen. The time from adding thedistilled water to drying the sample was less than 5 minutes.

The dried product was then mixed with 2M K₂ CO water solution. Thevolume of the solution was approximately 5 times the bulk volume of thedried carbonaceous material. The sample remained in the K₂ CO₃ solutionfor 30 minutes. The mixture was then centrifuged again. The excess waterwas removed and the wet sample transferred to a watch glass and placedinto 120° C. nitrogen for overnight drying.

The carbonaceous product thus obtained contained Li₂ CO₃ according toXRD analysis. Elemental analysis indicated that the lithiumconcentration in the product was 14% by weight.

It is believed that the carbonaceous reaction product containing themetal carbonate can be further processed to yield useful reactionproducts. Placing the C(MCO₃,O) in a reducing environment, such asreaction with magnesium or aluminum, would produce a product comprisingcarbon and elemental metal.

Heating the C(MCO₃,O) causes the metal carbonate to dissociate. If theheating is done in air, the final reaction product would be the metaloxide. If the heating is done in an inert environment, the finalreaction product would be metal oxide particles in carbon.

ALTERNATE EMBODIMENTS

The presence of bromine in the reaction product of EXAMPLE II suggeststhat the doping may be done by exposing the graphite oxide to dopantsalong with the metal chloride. Also, the dopants may include one or moremetal chlorides.

Washing the C(M,O,Cl) with distilled water reduces the particle sizes ofthe non-carbon content and could thereby increase the surface area ofthe carbonaceous reaction product.

The present invention has been described with reference to the preferredembodiment. Obviously, modifications and alterations will occur toothers upon a reading and understanding of the specification. It isintended by the applicant to include all such modifications andalterations insofar as they come within the scope of the appended claimsor the equivalents thereof.

Having thus described the invention,

What is claimed is:
 1. A process for producing material comprising metalcompounds from graphite oxide comprising the steps of:providing graphiteoxide; exposing the graphite oxide to a metal chloride at or below thethermal decomposition temperature of the graphite oxide for sufficienttime to form an intermediary carbonaceous reaction product comprisingelements of metal, oxygen, and chlorine; and removing the chlorine fromthe intermediary carbonaceous reaction product by placing theintermediary reaction product in an aqueous solution including at leastone member of the group consisting of potassium carbonate and sodiumcarbonate for a time sufficient to remove the chlorine and produce acarbonaceous reaction product comprising metal carbonate and oxygen. 2.The process of claim 1 further comprising the step of:placing thecarbonaceous reaction product comprising metal carbonate and oxygen inan inert environment at sufficient temperature for sufficient time tosubstantially remove the oxygen and convert the metal carbonate intometal oxide to produce a carbonaceous reaction product comprising metaloxide particles.
 3. The process of claim 1 further comprising the stepof:placing the carbonaceous reaction product in a reducing environmentat sufficient temperature for sufficient time to remove the oxygen andcarbonate and thereby produce a product comprising carbon and elementalmetal.
 4. The process of claim 1 further comprising the step of:heatingthe carbonaceous reaction product in air at sufficient temperature forsufficient time to dissociate the metal carbonate and remove the carbonand thereby produce a metal oxide product.
 5. A process for producingmaterial comprising metal compounds from graphite oxide comprising thesteps of:providing graphite oxide; exposing the graphite oxide to AlCl₃by initially maintaining the temperature at about 120° C. for up to 18hours; and, thereafter increasing the temperature up to 180° C. for upto six hours, thereby forming an intermediary carbonaceous reactionproduct comprising elements of metal, oxygen, and chlorine; and removingthe chlorine from the intermediary carbonaceous reaction products.
 6. Aprocess for producing material comprising metal compounds from graphiteoxide comprising the steps of:providing graphite oxide; exposing thegraphite oxide to AlCl₃ in a solution of bromoform by maintaining thetemperature at or near 100° C. for up to 115 minutes, thereby forming anintermediary carbonaceous reaction product comprising elements of metal,oxygen, and chlorine; and removing the chlorine from the intermediarycarbonaceous reaction product.
 7. A process for producing materialcomprising metal compounds from graphite oxide comprising the stepsof:providing graphite oxide; exposing the graphite oxide to AlCl₃ in asolution of bromoform by maintaining the temperature at about 20° C. forup to 115 minutes, thereby forming an intermediary carbonaceous reactionproduct comprising elements of metal, oxygen, and chlorine; and removingthe chlorine from the intermediary carbonaceous reaction product.